• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.637-640
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• 2008

Noise generated from maglev vehicles mainly consists of two components, one is due to mechanical noise and the other due to aerodynamic noise. The former is due to the vehicle-guideway interactions and the latter results from the unsteady air flow around the vehicle. Aerodynamic noise could become more predominant around 225 km/h for maglev vehicles. In this paper, the aerodynamic noise of maglev vehicles is investigated experimentally. The results of the wind tunnel experiments of maglev vehicle models are introduced and compared. The comparison shows that the position of the main noise is between the bottom of the vehicle model and the rail. It is also found that the emitted sound pressure level is related to the gap size between the vehicle bottom and the rail.

• Journal of Advanced Marine Engineering and Technology
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• 제31권8호
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• pp.947-953
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• 2007

Occurrence of pressure pulsation in positive displacement hydraulic turbine is one of the principal problems which should be cleared to improve the turbine performance and to put the turbine to practical use. Therefore, present study is tried to examine the occurrence mechanism and characteristics of the pressure pulsation CFD analysis and experimental measurement are implemented in this study to clarify the phenomena of unsteady pressure pulsation. The results show that occurrence reason of the pressure pulsation is not only due to a series of opening and closing of the chamber formed between rotor and casing wall but also due to the variation of rotational speed of following rotor. The pressure pulsation causes torque variation and the curve patterns of the torque variation conforms to that of the pressure pulsation. Pressure in the chamber is equal to the averaged value of inlet and outlet pressures. Sudden pressure decrease by accelerated through-flow between lobe and casing wall results in torque loss.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 추계 학술대회논문집
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• pp.109-113
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• 2002

Numerical analysis of aerodynamic heating for KPSAM is performed using aerodynamic heating model suitable to KPSAM, which has complex flow field resulting from the spike attached to the dome, such as large separation area and the strong shock/boundary layer interaction region around reattachment point on the dome. The aerodynamic heating model is validated and modified through the comparison between the flight test measurement and the thermal analysis results. TFD temperature sensors are installed on the dome to measure surface temperature during the flight. Computation results, obtained from the heat transfer analysis on the sensors, agree well with flight test data. The aerodynamic heating model provides heat transfer rate into surface as a boundary condition of unsteady 1D/axisymmetric thermal analysis on the missile structure. The axisymmetric thermal analysis using FLUENT is more versatile than the 1D analysis and can be applied to the heating problem related with complex structures and multi-dimensional heat transfer problems such as prediction of temperature rise at contact surface of different materials.

• 대한조선학회논문집
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• 제43권4호
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• pp.422-430
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• 2006

The horn and movable parts around the gap of the conventional semi-spade rudder are visualized by high speed CCD camera with the frame rate of 4000 fps (frame per second) to study the unsteady cavity pattern on the rudder surface and gap. In addition, the pressure measurements are conducted on the rudder surface and inside the gap to find out the characteristics of the flow behavior. The rudder without propeller wake is tested at the range of $1.0{\leq}{\sigma}_v\;1.6$ and at the rudder deflection angle of $-8{\leq}{\theta}{\leq}10^{\circ}$. The time resolved cavity images are captured and show strong cavitation around the rudder gap in all deflection angles. As the deflection angle gets larger, the flow separated from the horn surface increases the strength of cavitation. The accelerated flow along the horn decreases its pressure and the separated flow from the horn increases the pressure abruptly. The pressure distribution inside the gap reveals the flow moving from the pressure to suction side. In the negative deflection angle, the turning area on the movable part initiates the flow separation and cavitation on it.

• 해양환경안전학회지
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• 제12권4호
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• pp.267-272
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• 2006

버터플라이 밸브는 선박에서 냉각수와 유류 계통 등에 범용으로 널리 사용되고 있다. 이 연구에서는 유량조정에 따른 배관계통의 버터플라이밸브 후류 유동특성을 규명하기 위하여 입자영상 유속측정장치를 이용하여 밸브개도에 따른 유선과 속도벡터 분포에 관한 정량적인 데이터를 확보하였다. 또한 밸브 주위 유동장의 압력성분을 고찰하기 위하여 개폐각도를 6가지 경우로 변화시켜 정압을 측정하였다. 그 결과 실험관 벽면에서 측정된 압력의 분포는 디스크가 전개 상태인 $0^{\circ}$에서 $45^{\circ}$까지는 입구 압력은 일정한 상태로 거의 변화하지 않았으나 약 $60^{\circ}$ 이상에서부터 압력 상승과 점차 급격한 변동현상이 나타났다. 특히, $75^{\circ}$ 부근에서는 상류에서 급격한 압력 상승 경향을 보인 반면 하류 측은 압력변동이 적게 나타났다.

• 대한기계학회논문집B
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• 제20권7호
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• pp.2315-2325
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• 1996

A compression wave is attenuated or distorted as it propagates in a tube. The present study investigated the propagation characteristics of the compression waves which are generated by a train in a high-speed railway tunnel. A Total Variation Diminishing (TVD) difference scheme was applied to one-dimensional, unsteady viscous compressible flow. The numerical calculation involved the effects of wall friction, heat transfer and energy loss due to the friction heat in the boundary layer behind the propagating compression wave, and compared with the measurement results of a shock tube and a real tunnel. The present results show that attenuation of the compression wave in turbulent boundary layer is stronger than in laminar boundary layer, but nonlinear effect of the compression wave is greater in the laminar boundary layer. The energy loss due to the frictional heat had not influence on attenuation and distortion of the propagating compression waves.

• 한국정밀공학회지
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• 제22권3호
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• pp.46-51
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• 2005

The vacuum cleaner motor runs at very high speed for suction power. Specially, motor power is provided by the impeller being rotated at very high speed. The centrifugal fan consists of the impeller, the diffuser, and the circular casing. Due to the high rotating speed of the impeller and small gap distance between the impeller and the diffuser, the level of noise in the centrifugal fan is at BPF(Blade Passage Frequency) and its harmonic frequencies. In order to calculate the sound pressure of centrifugal fan, unsteady flow data are needed. The cause of noise is obtained by dividing the fluid noise by exhaust flow of fan and vibration noise by rotational vibration of vacuum cleaner fan motor. Until now, an accelerometer has been used to measure vibration. However, it can not measure vibration in some parts of brush and commutator because of motor construction and 3-D vibrating mode. This study was conducted to perform accurate analysis of vibration and aerodynamic sound for fan motor in a vacuum cleaner using a laser vibration analyzer. A silent fan motor can be designed using the data measured in this study.

• 대한기계학회논문집B
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• 제26권5호
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• pp.629-639
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• 2002

In-vitro flow characteristics downstream of a polyurethane artificial heart valve and a Bjork-Shiley Monostrut mechanical valve have been comparatively investigated in pulsatile flow using particle image velocimetry (PIV). With a triggering system and a time-delayed circuit the velocity distributions on the two perpendicular measurement planes downstream of the valves are evaluated at any given instant in conjunction with the opening behaviors of valve leaflets during a cardiac cycle. The regions of stasis and high shear stress can be found simultaneously by examining the entire view of the instantaneous velocity and Reynolds shear stress fields. It is known that high shear stress regions exist at the interface between strong axial jet flows along the wall and vortical flows in the central area distal to the valves. In addition. there are large stagnation or recirculation regions in the vicinity of the valve leaflet, where thrombus formation can be induced by accumulation of blood elements damaged in the high shear stress zones. A correlation between the unsteady flow patterns downstream of the valve and the corresponding opening postures of the polyurethane valve membrane gives useful data necessary for improved design of the frame structure and leaflet geometry of the polyurethane valve.

• Wind and Structures
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• 제18권2호
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• pp.155-180
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• 2014

The safety of road vehicles on the ground in crosswind has been investigated for many years. One of the most important fundamentals in the safety analysis is aerodynamic characteristics of a vehicle in crosswind. The most common way to study the aerodynamic characteristics of a vehicle in crosswind is wind tunnel tests to measure the aerodynamic coefficients and/or pressure coefficients of the vehicle. Due to the complexity of wind tunnel test equipment and procedure, the features of flow field around the vehicle are seldom explored in a wind tunnel, particularly for the vehicle moving on the ground. As a complementary to wind tunnel tests, the numerical method using computational fluid dynamics (CFD) can be employed as an effective tool to explore the aerodynamic characteristics of as well as flow features around the vehicle. This study explores crosswind effects on a high-sided lorry on the ground with and without movement through CFD simulations together with wind tunnel tests. Firstly, the aerodynamic forces on a stationary lorry model are measured in a wind tunnel, and the results are compared with the previous measurement results. The CFD with unsteady RANS method is then employed to simulate wind flow around and wind pressures on the stationary lorry. The numerical aerodynamic forces are compared with the wind tunnel test results. Furthermore, the same CFD method is extended to investigate the moving vehicle on the ground in crosswind. The results show that the CFD results match with wind tunnel test results and the current way using aerodynamic coefficients from a stationary vehicle in crosswind is acceptable. The CFD simulation can provide more insights on flow field and pressure distribution which are difficult to be obtained by wind tunnel tests.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2006년도 추계학술발표회
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• pp.265-269
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• 2006

파랑에 의한 선박의 횡동요를 방지하는 감요장치는 크게 수동식과 능동식 으로 분류할 수 있으며 수동형 감요수조는 선박에서 가장 널리 사용되고 있다. 이 연구에서는 감요장치의 하부덕트유동에 관한 기초연구로서 덕트의 제어 댐퍼와 유입부의 유통에 대해 입자영상 유속측정장치를 이용하여 속도벡터분포에 관한 정량적인 데이터를 확보하였다. 그 결과 실험관 벽면에서 측정 된 압력의 분포는 디스크가 전개 상태인 0 도에서 45도까지는 입구 압력은 일정한 상태로 거의 변화하지 않았으나 약 60도 이상에서부터 압력 상승과 점차 급격한 변동현상이 나타났다.